The present invention relates to a detection circuit, a physical quantity detection apparatus, an angular velocity detection apparatus, an integrated circuit device, and an electronic instrument.
A gyro sensor is provided in various electronic instruments such as a digital camera, a navigation system, and a mobile phone. An image stabilization process, a dead reckoning process, a motion sensing process, or the like is performed based on the magnitude of the angular velocity detected by the gyro sensor.
In recent years, a reduction in size and an increase in detection accuracy has been desired for a gyro sensor. For example, a vibrating gyro sensor that utilizes the resonance phenomenon of a crystal vibrator has been widely used as a gyro sensor that meets such a demand. Since the detection signal output from the vibrator becomes small along with a reduction in size of such a vibrating gyro sensor, it is very important to reduce noise generated by a signal processing circuit that performs a drive process and a detection process in order to implement high detection accuracy.
The detection process performed by the signal processing circuit includes amplifying and synchronously detecting a small detection signal output from the vibrator, and removing a harmonic component and high-frequency noise using a low-pass filter. The resulting detection signal is output to the outside via an output buffer. The output buffer adjusts the level of the detection signal according to the desired detection sensitivity. A switched capacitor filter (SCF) for which the frequency characteristics are determined by the capacitance ratio and the sampling frequency (clock frequency) is used as the low-pass filter. The switched capacitor filter has an advantage in that a variation in characteristics is small as compared with an RC filter (see JP-A-2008-14932 and JP-A-2008-64663).
Since noise that occurs in the low-pass filter is significantly small as compared with noise that occurs in the preceding stage of the low-pass filter, measures for reducing noise that occurs in the preceding stage of the low-pass filter have been mainly employed. However, since noise that occurs in the low-pass filter relatively increases due to a decrease in noise that occurs in the preceding stage of the low-pass filter, the S/N ratio of the output signal may deteriorate. It is difficult to reduce noise that occurs in the low-pass filter without significantly increasing the circuit area. Therefore, it may be impossible to meet a demand for a reduction in size when it is desired to further reduce noise. The amplification factor of noise that occurs in the low-pass filter may be decreased by decreasing the gain of the output buffer by increasing the gain in the preceding stage of the low-pass filter. However, it may be impossible to increase the gain in the preceding stage of the low-pass filter depending on the design.